Method and device for thermal destruction of organic compounds by an induction plasma

ABSTRACT

A method and device for chemical destruction of at least one feed comprising at least one organic compound are provided. The device comprises at least one inductive plasma torch, means for introducing at least one plasma-forming gas into the torch, optionally when the plasma gas(es) comprise(s) no or little oxygen, means for bringing oxygen gas into the plasma or into the vicinity of the plasma, means for introducing the feed into the torch, a reaction enclosure capable of allowing thermal destruction of the gases flowing from the torch, a device allowing mixing of the gases flowing out of the reaction enclosure to be carried out, means for introducing air and/or oxygen gas into the mixing device, a device allowing recombination by cooling of at least one portion of the gases from the mixing device, the torch, the reaction enclosure, the mixing device and the recombination device being in fluidic communication.

TECHNICAL FIELD

The present application relates to a method and to a device for thermaldestruction of organic compounds by an induction plasma.

More specifically, the invention relates to a method and device forthermal destruction of a feed, charge, load, comprising at least oneorganic compound, by means of at least one induction plasma formed by atleast one plasma gas ionized by an inductor or a inductive turn.

The feed may be composed of wastes and may notably be found in liquid,gas or powdery form, this may in particular be a radioactive feed.

The organic compounds may be harmful, toxic or dangerous compounds suchas hydrocarbons or organochlorinated products.

The technical field of the invention may generally be defined as that ofthe destruction of wastes by a thermal treatment, and more particularlyas that of the destruction of wastes by means of an induction plasma.

STATE OF THE PRIOR ART

The problem of treating wastes has been crucially posed for about tenyears. Indeed, the majority of the wastes were, in the past, simplydeposited in dumps, and therefore no real management of these wastes wascarried out.

But now, changes in the nature and amount of wastes have led to adoptingan industrial approach in order to carry out their treatment.

Numerous technologies are thus applied for treating wastes so thatdevelopment may continue without being harmful to the environment. Thesehigh performance technologies for destroying wastes have in common thatthey comprise both a method for destroying the wastes, treatments of thefumes produced during this destruction and management of the liquid orsolid residues which are possibly obtained.

Generally, thermal methods for destroying wastes are used in order toovercome the problem posed by the stability of many chemical compounds.Thus, installations for destroying dangerous products are traditionallyincinerators, in which, for example, liquid products are mixed withsolid products in order to be burned.

However by incinerating the wastes, volatile residues are obtained whichfurther need to be removed.

Moreover, these installations require sizeable volumes for allowingcomplete reactions between the fuel and the comburent, oxidizer and forreducing operational costs.

In order to find a remedy to these drawbacks, many methods fordestroying wastes use plasma technologies. Indeed, methods applying aplasma have the advantage of allowing reduction in the size of therequired installations since plasma incinerators give the possibility ofattaining very high temperatures and of therefore accelerating thechemical reactions for destroying the wastes and for recombining thethereby obtained chemical elements.

In document [1], efforts are made for destroying organic products bymeans of a blown arc plasma. The gases from the combustion of the wastesare mixed with air, water or oxygen at the outlet of the plasma torch ina segmented tubular stage. This technique allows destruction of gaswastes in an easy way by mixing the wastes with the plasma gas from thearc torch. Nevertheless, the efficiency of the method is reduced becausethe feeds to be destroyed do not pass into the torch. Destruction ofliquid products proves to be more complicated since it is difficult tohomogeneously mix a liquid phase in a gas phase at a high temperatureand at a high speed from a blown plasma arc torch. This difficultyfurther reduces the thermal yield and efficiency of the method.

Another example of the use of blown arc plasmas is shown in documents[2] and [3]. The wastes to be destroyed are introduced into a tubulartorch with a blown arc plasma after having been subjected to a change ofstate into a gas phase by means of an initial burner.

In the technique discussed in document [2], the fact of vaporizing thefeed in order to have it pass into the plasma torch, gives thepossibility of both increasing the destruction efficiency of the methodand considerably complicates the method, since it imposes constantmonitoring of proper vaporization of the feed. Addition of a gas burner,which requires a substantial air supply in order to operate properly,leads to a large gas flow rate in which the mass proportion of the feedis reduced.

The method described in document [3] allows introduction of the feed tobe destroyed, whether it be liquid or gaseous, directly into the plasmatorch. This method uses the technology for stabilizing the electric arcin the torch by means of an electromagnetic field. As this method is asubstantial consumer of electrical energy, it is reserved to destructionof products present in a very large amount. Further, no mention is madeof the type of gas used for operating the torch or for controllingatomic recombinations. Thus, this method carries out destruction of theproducts by pyrolysis, i.e. without any oxygen supply, which leads tostrongly reducing gases being obtained which have to be burned at theoutlet of the torch before being discharged into the atmosphere.

In document [4], the wastes are mixed with water or with methanol andare introduced into a tubular arc torch. Oxygen, instead of air is alsoused as a plasma gas. The purpose of these modifications is to improvethe efficiency of destruction of the wastes. In this document, a tubularsegmented arc torch is used. This is a relatively uncommon technologywhich requires good knowledge of plasma technology in order to definestable operating parameters. The use of two phases, a liquid and gasphase, in this type of technology does not facilitate the establishmentof stable operation.

In document [5], a plasma burner is used for purifying and cleaning upgases flowing out of a conventional incinerator. High temperaturepost-combustion with injection of air in the mixing chamber with gasproducts to be neutralized is thereby achieved. Again, with this method,the plasma torch is used as an extra energy carrier for purifying gases.Therefore, it is not possible to treat liquids directly without havingvaporized them beforehand in a conventional incinerator for example.

Moreover, the fact of not introducing the feed within the torch, formaterial incompatibility reasons, strongly reduces the efficiency of themethod.

It is also possible to use radiofrequency or high frequency plasmas. Forexample, in document [6], the solid products to be destroyed are firstintroduced into a rotary kiln so as to be transformed into a gas form.The gas flow is then directed towards a collector where it is mixed witha carrier gas and optionally with liquid wastes. This mixture is thenintroduced into a high frequency plasma torch. The products from thetorch then pass into a centrifuge provided with a toric system forgenerating electric and magnetic fields. With this system, it is thenpossible to separate the different elements.

This technique has as a primary purpose, the separation of the differentconstituents of feeds with optional recovery of recyclable valuableproducts such as heavy elements.

The torch has a particular geometry into which the feeds are introducedvia an undefined collector. The attained field temperatures which arefrom 300 to 1,000° C. do not allow destruction in the strict sense ofthe term but rather allow conditioning for separation of the differentelements.

Document [7] relates to the destruction of toxic gas products ofmilitary origin by means of a plasma torch operating under an air/argonmixture.

At the outlet of the torch, an air/water quenching mixture is introducedin order to stop the reactions. The feeds to be destroyed either passinto an inerting module, or into the plasma module. Thus, it appearsthat it is mainly the gases that are directed towards the plasma module.The introduction of liquid is only a possibility depending on thecomposition of the feed.

Most methods for destroying wastes as described above use plasma arctorches which are positioned in specific reactors and for which thewaste destruction efficiency is insufficient.

This is why, in order to substantially improve these destructionefficiencies, a method was developed in which a liquid or powderyorganic or organo-halogenated compound to be destroyed is mixed withwater and introduced with a plasma-forming gas into the core of aninductive plasma torch. In other words, this method is based on the useof an induction plasma torch into the inside of which the feed ofcompounds to be destroyed is introduced. This method ensures destructionof the feed by introduction of water which is sprayed into the plasmawith the compounds to be destroyed.

This method is described in document FR-A1-2 966 414 [8] and the devicefor its application is illustrated in FIG. 1.

This device comprises an induction plasma torch supplied with a plasmagas (1) ionized by means of an inductor (2) in order to thereby form aplasma (3).

This torch is equipped upstream with a system (4) for introducing thefeed to be treated. In order to ensure compliant destruction of thefeed, water is mixed with the introduced feed (5).

Dissociation of water at a very high temperature ensures the oxygensupply required for oxidizing the organic or organo-halogenated specieson the one hand and a hydrogen supply required for forming HCl on theother hand.

The first claim of document [8] indicates on this matter that theorganic product is mixed with water in a sufficient amount in order toat least satisfy the stoichiometric ratios between the carbon and oxygenatoms of the mixture, or that the organo-halogenated product is mixedwith water in a sufficient amount in order to at least satisfy thestoichiometric ratios between the carbon and oxygen atoms of the mixtureon the one hand, and between the hydrogen and halogen atoms of themixture, on the other hand.

Indeed, a lack of hydrogen in the medium may be at the origin of theproduction of undesirable molecules such as phosgene COCl₂. The plasma(3) generates many highly reactive ionic species which ensure thedestruction of the organic compounds. These destruction reactions occurin the reactor (6) which is maintained at a very high temperature thanksto refractory materials (7) which line its internal walls (8).

Introduction of air and/or oxygen (9, 10) at the bottom of the reactorand at a venturi (11) ensures significant mixing of the gases and anadditional supply of oxygen.

Next, the gases are rapidly cooled before entering a recombination area(12) in which the last reactions occur.

The gases are then directed (13) towards a treatment notably consistingin neutralization of the acid species.

A pilot installation was set into place in order to test the efficiencyof the method described in document [8]. The power of the plasmagenerator is 4.5 kW for an effective power in the plasma from 1 to 1.5kW.

If degradation of the products is very satisfactory, the energyefficiency of the method may be described as average or even poor,because of the large amount of water to be heated and to be volatilized.

Two reference molecules, taken as an example, were treated in the pilotinstallation in which they were each supplied at a rate of 100 g/h:

-   -   trichloromethane or chloroform of formula CHCl₃,    -   chlorobenzene of formula C₆H₅Cl.

Treatment of chloroform requires a water supply of a minimum of about 30g/h for a treatment heat balance of about 100 W. The power available inthe torch is thus widely sufficient for ensuring complete treatment ofthe solvent.

Treatment of chlorobenzene requires a water supply of a minimum of about200 g/h for a treatment heat balance of about 550 W. If the power in theplasma is still sufficient, the available margin is more limited. If theamount of water is brought to twice the stoichiometry for securing,guaranteeing the treatment, the heat balance increases to approximately900W which reduces the energy margin to almost 0.

Being aware that for reasons of reaction efficiency, it is reasonable towork with at least double water stoichiometry, the energy yield iswidely reduced.

As an illustration, FIG. 2 illustrates the time-dependent change in themaximum treatment flow rate of an aliphatic chlorinated solvent CxHyClper available kW in the plasma.

It should be noted that the calculations were carried out with solventscomprising aliphatic chains with a single chlorine atom (z=1). But theconclusions would be identical with a number of chlorine atoms zdifferent from 1.

It appears that this flow rate substantially decreases with the numberof carbon atoms x, which makes the method moderately or not veryattractive for a large scale industrial application.

From the foregoing, it therefore emerges that the method and the devicewhich are described in document [8] have certain drawbacks which arenotably the following:

-   -   an insufficient energy yield of the method;    -   a limited feed rate;    -   the use of a costly plasma gas such as argon which makes the        method not very interesting within the scope of an industrial        application;    -   difficulties for treating and destroying compounds which are        non-miscible with water.

Therefore, there exists a need for a method and a device for destroyinga feed comprising at least one organic compound by means of at least oneinduction plasma formed by at least one plasma-forming gas ionized by aninductor, which do not have the drawbacks of the method and of thedevice described in document [8].

The goal of the present invention inter alia is to provide a method anda device for destroying a feed comprising at least one organic compoundby means of at least one induction plasma formed by at least oneplasma-forming gas ionized by an inductor which inter alia meet thisneed.

The goal of the present invention is further to provide such a methodand such a device which do not have the drawbacks, defects, limitationsand disadvantages of the methods and devices of the prior art such asthe method and the device described in document [8].

DISCUSSION OF THE INVENTION

This goal and still other ones are achieved according to the inventionby a method for thermal destruction of at least one feed comprising atleast one organic compound by at least one induction plasma formed by atleast one plasma-forming gas ionized by an inductor, wherein thefollowing successive steps are carried out;

a) said feed is introduced into the plasma, and a supply of oxygen gasis achieved in said at least one plasma-forming gas, and/or in theplasma or in the vicinity of the plasma, by means of which gases areobtained in which decomposition into atomic elements has been induced;

b) in a reaction enclosure, a first operation for thermal destruction ofsaid gases in which decomposition into atomic elements has been induced,is carried out;

c) a second operation for thermal destruction of the gases havingundergone the first operation for thermal destruction is carried out, bymixing of said gases with air and/or with oxygen;

d) a recombination is achieved by cooling at least one portion of thegases from the mixing;

e) the gases are discharged.

Advantageously, the supply of oxygen gas may be achieved by using pureoxygen as a single plasma-forming gas.

In other words, the plasma-forming gas(es) is(are) then composed of pureoxygen.

It is then generally not necessary to achieve a supply of oxygen gas inanother way, for example by bringing oxygen gas into the plasma or intothe vicinity of the plasma.

If the plasma-forming gas(es) is(are) not composed of oxygen, does(do)not comprise oxygen or comprise(s) little oxygen, the supply of oxygengas may then be achieved by bringing oxygen gas into the plasma (alreadyformed) or into the vicinity of the plasma (already formed).

By plasma, is meant the plasma already formed, already made up. Theplasma already formed, already made up, should not be mistaken forplasma-forming gas(es).

By plasma-forming gas(es) comprising little oxygen, is generally meantthat the amount of oxygen in the plasma-forming gas(es) is notsufficient for having decomposition into atomic elements and the firstand second thermal destruction operations occur under satisfactoryconditions.

Advantageously, when the plasma gas(es) is(are) not composed of oxygen,does(do) not comprise oxygen or comprise(s) little oxygen, the supply ofoxygen gas may be achieved by introducing oxygen gas into the plasma ata location identical or close to the location where the feed isintroduced, and simultaneously with the latter.

Advantageously, the molar ratio of the oxygen gas supplied to theorganic compound(s) is greater than the stoichiometric combustion ratio.

Advantageously, in step c), mixing may be achieved with a venturi deviceinto which air and/or oxygen gas is(are) injected.

Generally, air and/or oxygen gas is systematically injected at themixing and there is cooling at the mixing.

Or else, notably but not only, in the case when the feed furthercontains at least one mineral filler, in step c), the mixing may beachieved by an air and/or oxygen distribution ring which injects airand/or oxygen gas towards the main axis of the reaction enclosure.

Advantageously, at the end of step d), at least one step d1) may beprovided for chemical treatment of the gases.

Advantageously, said at least one step d1) for chemical treatment of thegases is selected from a dehalogenation or neutralization step, a stepfor deoxidation of nitrogen oxides and a desulfuration step.

Advantageously, when the feed further contains at least one mineralfiller, a gas filtering step may be provided after step d) and beforestep d1).

Advantageously at the end of the step for chemical treatment of thegases d1), the gases may be treated in a droplet catcher condenser.

Advantageously, several either identical or different feeds may betreated with several plasmas.

The method according to the invention may be defined as a modificationor rather as an improvement of the method described in document [8].

According to the invention, the method of document [8] was modified inorder to apply as an oxidizer, comburent, oxygen instead and in place ofwater.

In other words, the modification of the method of document [8] which isthe object of the present invention mainly consists of adapting themethod of document [8] so that it only operates with pure oxygen as aplasma-forming gas which then has the dual function of a plasma-forminggas and of an oxidizing, comburent, gas; or else with a plasma-forminggas comprising no or little oxygen and with an oxygen supply.

In other words, according to the invention only the feed is introducedinto the plasma and the feed is not mixed with water before itsintroduction into the plasma, as this is the case in document [8].

In the method according to the invention, destruction of the organiccompounds is ensured by the introduction, arrival, admission, supply ofoxygen gas. This introduction may ideally be ensured by the plasma, inthe case when pure oxygen is used as a single plasma-forming gas (seeFIG. 6).

Or else, this introduction of oxygen may be ensured via an auxiliaryinlet, the plasma then being composed of one or several other gases notcomprising oxygen or comprising little oxygen (see FIG. 7).

The method according to the invention includes a series of specificsteps which has never been described or suggested in the prior art.

In particular, implementation in a method for thermal destruction ofwastes using an induction plasma, of oxygen as an oxidizer, comburent,instead of water, has never been described or suggested in the prior artand notably in document [8] mentioned above.

The method according to the invention does not have the drawbacks,defects, limitations and disadvantages of the methods of the prior artand provides a solution to the problems of the method of the prior artand notably of the methods of document [8].

It should first of all be noted that replacement of water with oxygenglobally has only little impact on the application of the method.

The method according to the invention may therefore be applied inexisting installations provided for operating with water as anoxidizing, comburent, gas, without it being necessary to deeply modifythese installations.

Only slight adaptations should possibly be made so that oxygen is usedas an oxidizer instead of water.

More specifically, if the interest lies in the treatment oforgano-halogenated compounds, it is known that the treatment oforgano-halogenated products with water is justified in order to avoidformation of highly toxic compounds such as phosgene COCl₂. Thiscompound is formed under a reducing condition between the chlorine atomsand the CO radicals. Introducing water imposes a certain hydrogenpotential required for binding these chlorine atoms in order to producehydrochloric acid HCl which is neutralized downstream in a washingcolumn as this is described in document [8].

Introducing oxygen into the system, like this is the case in the methodaccording to the invention, imposes more oxidizing conditions but limitsthe binding capabilities of chlorine.

A study conducted on the molecule CHCl₃, highly loaded with chlorineshows that for treating one mole of product, the amount of COCl₂ formeddepends on the amount of introduced oxidizer, comburent. Below the ratio1/1, it appears that phosgene is formed in both cases with a maximumamount 3 times greater during a treatment with oxygen. On the otherhand, when the ratio is greater than 1/1, phosgene no longer forms. Inthe case of the treatment with water, beyond this ratio, the hydrogenpotential is sufficient for reacting with the chlorine in order to formHCl which will be neutralized subsequently. In the case of the oxygentreatment, beyond this ratio, the oxygen potential is sufficient forgasifying the totality of the carbon in the form of CO₂.

The conclusion is that regardless of the oxidizer, comburent, used,phosgene is formed under sub-stoichiometric conditions. When thestoichiometry is exceeded, this toxic compound disappears. FIG. 3illustrates this result through the treatment of 1 mole of chloroform.

The difference between both operating modes lies in the formation ofchlorine Cl₂ during treatment with O₂ as this appears in FIG. 4. In thecase of a treatment with water, this amount is reduced to zero when theratio attains 1/1.

It might be believed that in the method according to the inventionoperating with oxygen, the installation for treating the gases,initially designed and proportioned for neutralizing hydrogen chlorideHCl, should be modified and re-proportioned in order to ensureneutralization of chlorine gas Cl₂.

Now, it is found that the latter is easily neutralized by a washingcolumn with soda while forming sodium chloride and sodium hypochloriteNaClO. The gas treatment system initially in place in the installationoperating with water therefore does not have to be modified. Only themanagement of the effluents downstream will generally have to take intoaccount the presence of this hypochlorite.

The method according to the invention has many advantages relatively tothe methods of the prior art, and notably to the method of document [8],advantages which are notably generally related to the replacement ofwater with oxygen in order to ensure combustion of the organicmaterials, compounds, whether oxygen constitutes the plasma-forming gasor not. These advantages are notably the following:

-   -   a very substantial improvement in the energy yield of the        method;    -   the possibility of treating all types of feeds and even liquid        feeds non-miscible with water, which was possible with        difficulty with the method described in document [8]. With the        method according to the invention, such liquids may be easily        introduced into the plasma and treated. The range of feeds which        may be treated by the method according to the invention is        therefore very extended and has almost no limitations;    -   a substantial increase in the feed level for a same size of        equipment.

The advantages of the method according to the invention are even morenumerous and even more notable in the case of a preferred embodiment ofthe method according to the invention where pure oxygen is used as aplasma-forming gas, i.e. in the case when water is replaced with oxygenwhich is also used as a plasma-forming gas. These advantages, some ofwhich have already been mentioned above, are notably the following:

-   -   first of all, the plasma-forming gases currently used are air,        nitrogen or argon. The use of air or nitrogen leads to a        significant production of nitrogen oxide which requires the        setting up of a catalytic reduction column downstream generally        using an ammonia solution. The use of argon as for it is costly        for an industrial utilization.

In this preferred embodiment of the method according to the invention,the use of pure oxygen as plasma-forming gas, substantially less costlythan argon and not leading to the production of nitrogen oxide is asolution of choice since, in addition to being the source of the plasma,it also ensures the oxygen supply required for combustion of the organiccompounds. In other words, it plays both the role of a plasma-forminggas and of an oxidizing, comburent, gas. Nitrogen-free, it also avoidsthe setting up of an additional unit for neutralization of thecorresponding oxides.

By using pure oxygen as a plasma gas, use of highly expensive argon forthis purpose is notably avoided, which has a strong impact on theoperating cost of the method.

-   -   improvement in the performance of the destruction of the wastes,        effluents and optimization of the combustion of the gases;    -   the possibility as already specified above of treating liquid        feeds non-miscible with water;    -   a substantial increase in the treatment capacity of the method.

More specifically, in the

water mode

, i.e. in the case of the method of document [8], the method is highly

energy-consuming

which limits the treatment flow rates.

For example, in the case of treatment of compounds of the aliphatichydrocarbons series C_(x)H_(y)Cl, the power required for treating a flowrate of 100 g/h increases with the number x of carbon atoms. In theoxygen mode, combustion of the organic materials releases power. On thebasis of a feed rate of 100 kg/h, this power substantially increaseswith the number x of carbon atoms.

The differences between both modes appear in FIG. 5. In the second case,the negative scale takes into account production of power. It isdeveloped by the combustion of the solvents and has to be compensated byincreasing the temperature of the reactor and optimizing the dissipationof the calories.

Within the scope of a large scale industrial operation, the powerdeveloped during the treatment may be utilized. For example, a unit fortreating 50 kg/h of a compound similar to chlorohexane will develop apower close to 450 kW.

The invention further relates to a device for destroying at least onefeed comprising at least one organic compound by at least one inductionplasma formed by at least one plasma-forming gas ionized by an inductor,comprising:

-   -   at least one inductive plasma torch;    -   means for introducing at least one plasma-forming gas into said        torch;    -   optionally when the plasma gas(es) is(are) not composed of        oxygen, comprise(s) no oxygen or comprise(s) little oxygen,        means for bringing oxygen gas into the plasma or to the vicinity        of the plasma;    -   means for introducing said feed into said torch;    -   a reaction enclosure, chamber, (7) capable of allowing thermal        destruction of the gases flowing out of the inductive plasma        torch (6);    -   a device allowing mixing of the gases flowing out of the        reaction enclosure, chamber (7) to be carried out;    -   means for introducing air and/or oxygen gas (9) into the mixing        device (8);    -   a device (10) allowing recombination by cooling, of at least one        portion of the gases from the mixing device (8);

the inductive plasma torch (6), the enclosure, reaction chamber (7), themixing device (8), and the recombination device (10) being in fluidiccommunication.

Advantageously, the means for introducing the feed into the torch mayconsist of a tube made of a refractory material, the inside of which ispacked with a textile made of fibers of a refractory material.

Advantageously, said tube made of a refractory material may furthercomprise in its centre a tube for bringing oxygen gas into the plasma.

Advantageously, the device allowing gas mixing to be performed, may be aventuri.

Or else, the device allowing mixing of the gases to be carried out, maybe a distribution ring which is capable of injecting air and/or oxygentowards the main axis of the reaction enclosure.

Advantageously, the device allowing recombination by cooling, of atleast one portion of the gases from the mixing device, may be awater-cooled double-walled enclosure.

Advantageously, the device may further comprise, located downstream fromthe gas recombination device in the circulation direction of the gases,at least one device allowing chemical treatment of the gases from therecombination device.

Advantageously, said at least one device allowing chemical treatment ofthe gases from the recombination device may achieve at least onereaction selected from a dehalogenation, a deoxidation of nitrogenoxides and a desulfuration.

Advantageously, the device may further comprise filtration meansdownstream from the gas recombination device in the direction ofcirculation of the gases, and upstream from said at least one deviceallowing chemical treatment of the gases from the recombination device.

Advantageously, the device may comprise several plasma torches.

Advantageously, the device may be placed on a vehicle.

The invention will be better understood and other advantages thereofwill become apparent upon reading the detailed description whichfollows, made as an illustration and not as a limitation, with referenceto the appended drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical sectional view of the device for carryingout the method described in document [8] which uses water as anoxidizer, comburent;

FIG. 2 is a graph which gives the maximum flow rate for treatingC_(x)H_(y)Cl compounds with water as an oxidizer, comburent. The maximumtreatment flow rate (in g/h/kW) is plotted in ordinates and the numberof carbon atoms x of the compound is plotted in abscissae.

FIG. 3 is a graph which shows the change in the formation of phosgeneCOCl₂ versus the amount and the nature of the oxidizer, comburent, used,respectively water or oxygen, during destruction of chloroform. Theamount of formed COCl₂ (in moles) is plotted in ordinates and the amountof oxidizer, comburent, for one mole of chloroform is plotted inabscissae.

FIG. 4 is a graph which shows the change in the formation of chlorineCl₂ versus the amount and the nature of the oxidizer, comburent used,water or oxygen respectively, during the destruction of chloroform. Theamount of formed Cl₂ (in moles) is plotted in ordinates and the amountof oxidizer, comburent for one mole of chloroform is plotted inabscissae.

FIG. 5 is a graph which shows the power required for treating 100 g/h ofa compound C_(x)H_(y)Cl versus the number of carbon atoms x of thecompound, for water and oxygen oxidizers, comburents, respectively. Thetreatment power for 100 g/h (in W) is plotted in ordinates, and thenumber of carbon atoms x of the compound C_(x)H_(y)Cl is plotted inabscissae.

A positive ordinate corresponds to power absorption and a negativeordinate corresponds to power production.

FIG. 6 is a schematic vertical sectional view of a device for carryingout the method according to the invention in an embodiment where theplasma-forming gas is composed of pure oxygen.

FIG. 7 is a schematic sectional view of a device for carrying out themethod according to the invention in an embodiment where theplasma-forming gas comprises no oxygen or little oxygen.

FIG. 8 is a schematic vertical sectional view showing the structure of aspecific rod designed in order to introduce a fluid feed into the coreof a plasma, and its application in a plasma torch.

FIG. 9 is a schematic vertical sectional view showing the structure of aspecific rod designed for introducing a fluid feed and an oxidizing gas,such as oxygen, into the core of a plasma, and its application in aplasma torch.

FIG. 10 is a schematic vertical sectional view which illustrates thewhole of a device for carrying out the method according to theinvention.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

Let us specify first of all that the method and the device according tothe invention are defined as being a method and a device for thermaldestruction of a load, feed, charge, comprising at least one organiccompound.

Preferably, the feed is composed of (consists of) said at least oneorganic compound.

According to the invention, the treated feed is generally a fluid feed,i.e. it is in liquid, gas or powdery form (i.e. in the latter case itforms a flowable powder).

By organic compound is generally meant a compound comprising, preferablycomposed of, consisting of, carbon and hydrogen atoms and optionallyatoms selected from oxygen, nitrogen, sulfur atoms and from halogenatoms such as chlorine, bromine, iodine and fluorine atoms.

The organic compound(s) to be destroyed are generally toxic, harmful ordangerous organic compounds for example explosive compounds; and/orradioactive compounds.

These compounds may for example be organo-halogenated solvents, notablyorganochlorinated solvents, oils, aromatic or aliphatic hydrocarbons,toxic gas products such as chlorofluorocarbons CFC orhydrochlorofluorocarbons HCFC, warfare gases, solid explosives etc.

A preferred feed which may be treated by the method according to theinvention is a radioactive liquid feed comprising halogenated organiccompounds, the structure of which includes radioactive tracers such as¹⁴C or ³H.

By destruction is meant that at the end of the method, i.e. generally inthe discharge gases, the organic compounds initially present in the feedand the removal of which is sought are no longer present or present witha content of less than 10% by mass, preferably less than 5% by mass, oreven that these compounds are no longer detectable and that theircontent may then be considered as zero. The organic compounds to bedestroyed are transformed in the method into molecules of smaller size,for which the harmfulness, toxicity, dangerousness is less than that ofthe compounds to be destroyed, initially present in the feed, or evenfor which the toxicity, harmfulness may be considered as nil.

FIG. 6 illustrates a device for carrying out the method according to theinvention in an embodiment where the plasma-forming gas is composed of,consists of, pure oxygen. The device of this figure is substantiallysimilar to the one of FIG. 1 (the same reference symbols are used),however except that the oxygen is used as plasma-forming gas and isintroduced into the reactor through the duct (1) opening out into theplasma torch, and that only the feed to be treated (5) is introduced,fed, into the plasma and not a mixture of the feed and of water.Further, advantageously, the introduction, feeding, system (4) of thedevice of FIG. 1 may optionally be replaced in the device according tothe invention by a specific introduction rod, tube (14), and/or theventuri (11) of the device of FIG. 1 may be suppressed and replaced by agas distribution ring for injecting air and/or oxygen (15) towards thecentre of the reactor as this is described in more detail below.

FIG. 7 illustrates a device for carrying out the method according to theinvention in an embodiment wherein the plasma-forming gas is not pureoxygen, or wherein the plasma-forming gas(es) comprise(s) no oxygen orlittle oxygen.

It is therefore necessary to provide an oxygen supply which may beaccomplished by directly bringing the gas into the core of the reactoror by bringing it simultaneously and jointly with the feed for examplethe liquid or gas feed to be treated. In the first case, and as this isillustrated in FIG. 7, tapping of a traditional type (16) gives thepossibility of ensuring the arrival of oxygen into the reactor as closeas possible to the plasma or into the plasma, while another separateduct (1) allows introduction of a plasma-forming gas into the plasmatorch. As for the remainder, the device of FIG. 7 is substantiallysimilar to the one of FIG. 6.

FIG. 10 shows the whole of a device for carrying out the methodaccording to the invention.

From upstream to downstream, the installation is equipped with aninduction plasma torch (102) powered by an electric generator (101)connected to the mains (380V/50 Hz) which delivers a high frequencycurrent adapted to the geometry of the torch (102).

Supplying power to the torch (102) with the generator (101) is generallyaccomplished via a control panel (not shown).

Starting of the torch (102) is ensured at atmospheric pressure bysetting up tungsten filaments (103) in the torch (102) which, when theyare subjected to the high frequency electromagnetic field, initiate theplasma.

In the case of an oxygen plasma, the starting may be accomplishedaccording to other means avoiding oxidization of the electrodes.

The torch (102) generally consists of one single coil, of a turn,generally cooled by air, which is supplied with oxygen by means ofsuitable inlets (104) and which is supplied with a feed by suitablemeans (105) which introduce the feed into the inside of the plasma.

Preferably and notably in the case when the feed is liquid, the meansfor introducing the feed into the plasma consist of a specific rod forintroducing liquids into the core of the plasma.

This specific rod, tube is illustrated in more detail in FIG. 8.

Indeed, a plasma is a viscous medium into which it is difficult tointroduce fluids.

The rod (81) plunges into the core of the plasma (82) and opens out (83)into the lower portion of the single inductive coil, inductive turn (84)where the feed (85) sent from the top (86) of the rod is therebyintroduced.

If reference is made to FIG. 8, this rod consists of:

-   -   a tube (87) made of a refractory material such as alumina, which        ensures the mechanical structure;    -   a packing or wick (88) composed of a textile made of fibers of a        refractory material such as a glass, alumina, or zirconia in        which the feed (85), generally fluid, is introduced through one        of the ends of the rod, which is generally its upper end (86)        because the rod is generally positioned vertically.

In this structure, the textile fibers packing (88) prevents theformation of drops falling through the plasma (82). It ensures a regularflow rate by capillary impregnation.

When the fluid is a liquid, the high temperatures attained by the rod inits middle portion ensure vaporization and the organic material isessentially treated in gas form.

However, this rod may also be used with fluids which are not liquid.

As this was already indicated above, the provision, supply of oxygen maybe accomplished in several ways. Thus, in the case when theplasma-forming gas is composed of oxygen, then the oxygen supplynaturally consists of the supply of this plasma-forming gas (FIG. 6).

Or else, if the plasma-forming gas comprises no oxygen or little oxygen,then the provision, supply of oxygen may be accomplished by bringing theoxygen gas directly into the core of the reactor or by bringing ittogether with the feed.

In the first case, a tapping of the traditional type ensures arrival ofoxygen into the torch which produces the plasma (FIG. 7).

The feed is brought into the plasma through the rod described in FIG. 8.

In the second case, oxygen may be brought in via the rod described aboveand in FIG. 8, this rod being modified so as to allow passage of oxygen.

This modified rod or dual, double rod (91) is shown in FIG. 9.

As oxygen cannot be mixed with the organic compounds of the feed beforetheir arrival into the reactor for safety reasons, a tube, generally acapillary tube (92), may be set up in the center of the rod (91) whichretains its textile or fibrous packing (88) described above. The oxygen(93) is then introduced into the capillary (92) while the feed (85)comprising the organic compounds is introduced through one of the endsof the rod, generally its upper end (86) at the periphery in the annularspace defined between the wall (94) of the tube bringing the oxygen andthe wall (87) of the rod.

The plasma formed in the plasma torch (102) burns in a reactor or in areaction enclosure (106).

This reaction chamber (106) generally includes a double wall in whichthe cooling water circulates. This double wall may be made of steel. Theinner surface of the double wall is covered with a protective refractorymaterial.

The external walls of the reactor are generally cooled by circulation ofwater.

The chemical species from the plasma oxidized in the reactor, reactionenclosure, (106) by means of the oxygen introduced into the torch (102)notably when pure oxygen is used as a plasma-forming gas. The reactionchamber has the function of confining the heat produced in the plasmatorch in order to thereby allow complete destruction of the waste. Thegas from this reaction enclosure may thus attain a temperature above1,500° C.

The reaction chamber is generally in the form of a vertical cylindershape at the top of which is positioned the plasma torch. Generally, thewalls of the reaction enclosure are thermally insulated by a refractorymaterial.

Said oxidation is promoted by means of a mixing device (107) such as aventuri, located at the lower portion of the reaction enclosure. Anintroduction of oxidizing, comburent gas for example air and/or oxygen(108) may be provided at this device.

In the case when the mixing device is a venturi, there is alwaysintroduction of air and/or of oxygen into the mixing device.

If the venturi is suppressed, only an introduction of air and/or oxygenby means of a distribution ring is retained.

The structure of the venturi is described in detail in document [8] tothe description of which reference may be made.

The venturi by means of a supply of oxidizing gas such as air and/oroxygen allows generation of a second combustion or post-combustionbetween this oxidizer, comburent and the gases from the reactionenclosure. With this device it is thus possible to destroy thecompounds, notably the toxic compounds which would have escaped thefirst destruction stage in the reaction enclosure (106).

In other words, the purpose of the venturi is to generate significantturbulence of the reaction gases from the reaction chamber (106) bymeans of a cold air and/or oxygen supply (108). This mixture of gasesconsisting of cold air and/or oxygen and reaction products, allowswithout any provision of additional heat, generation of post-combustionof the gases from the reaction chamber. It is thus possible to completethe destruction of the possible reactive gases which have not beentransformed in the reaction chamber (106). In the venturi, the differentgas species such as H₂, CO, C . . . will react with air according to thefollowing reaction:

CO+H₂+O₂→CO₂+H₂O

The harmful gas CO is thus transformed into a less harmful gas.

It may be stated that the venturi notably ensures mixing for improvingthe recombination rates, speeds and cooling by addition of air and/oroxygen (108).

In the case when the fluid includes mineral fillers, the venturi issuppressed, introduction of air also ensures quenching of the gases andof the particles found therein.

According to the invention, the geometry of the reactor, reactionenclosure, may be modified, at the mixing device (107), in order toallow the reactor to more easily accept mineral fillers.

Indeed, the method according to the invention is generally dedicated tothe treatment of fluids without any mineral fillers.

However, for example, the treatment of used solvents having been usedfor dissolving materials containing minerals results in theconcentration of these mineral fillers in the form of particles whichmay form deposits.

The presence of the venturi, present in order to ensure substantialmixing of the gases risks being at the origin of the formation ofdeposits and of a plug. This is why the treatment of liquids loaded withminerals should preferably be carried out with a reactor of a differentdesign.

In this embodiment, the venturi is removed in order to avoid unwanteddeposits at its level. It is replaced by a ring for distributing gases,for example air which may be enriched in oxygen. Said ring injects airand/or oxygen towards the axis of the reactor (which generally appearsas a vertical cylinder) in a direction which may be tilted upwards. Thistilt will depend on the geometry of the reactor and on the power of theplasma torch used. It may range from 0° to 70° relatively to thehorizontal depending on the case.

The gas, the injection pressure of which may be modulated according tothe geometry of the reactor and the power of the plasma, will have thefunction of generating a rupture area in the flow and of imposing theturbulence required for proper mixing. It will also ensure quenching ofthe gases and of the liquid particles which may be found therein inorder to limit the formation of coherent deposits which may degrade theoperation of the method. The gas distribution ring ensurespost-combustion as this is the case in the venturi.

The treatment of liquids which may contain mineral fillers shouldinvolve a filtration step downstream from the reactor. A filter (112)will therefore have to be introduced into the chain for treating gases.

This configuration of the reactor with a gas distribution ring is shownin FIGS. 6 and 7. The additional filter is not illustrated but isincluded in the treatment of the gases.

Downstream from this mixing device (107) the gases penetrate into acooler (109) which brings the gases to a temperature compatible with thetreatment device positioned downstream.

This cooler (109) also allows the gases to finish their recombinationprocess which has already begun in the venturi. By recombination ismeant that the organic compounds which have been destroyed in theplasma, oxidized by oxygen, are recombined in small molecules forming agas which may generally be discharged into the atmosphere aftertreatment, for example, a neutralization treatment for removing certainspecies such as HCl or Cl₂.

This cooler (109) which may also be called a recombination space,generally consists in a double wall chamber cooled by water. In thisspace, the temperature of the gases rapidly drops so as to attain forexample 200° C. at the outlet. Unlike the reaction enclosure (106), therecombination space is not thermally insulated and its double wall iscooled by circulation of water from a central cooling unit. In thisspace, the gases flow and cool by natural convection close to the walls.

At the outlet of the cooler, or recombination space (109), the gases areanalyzed for example by mass spectrometry or by infrared spectroscopy(118). With this analysis it is possible to check the efficiency of theheat treatment and to know the composition of the gases after this heattreatment, but especially with the analysis, it is possible to knowwhether the gases additionally have to undergo at least one chemicaltreatment.

The temperature of the gases may be adjusted by spraying water (111) atthe inlet of an

oversleeve

(110) before directing the gases towards the gas treatment installation(113). It is thus possible to lower the temperature of the gases in thecase of excess heat notably for protecting the system for neutralizationof the halogens.

This gas treatment installation (113) is adapted according to thecompounds which have to be treated. In this installation, it is possibleto carry out one or several chemical treatments of the gases, selectedfor example from a dehalogenation treatment or treatment for removingthe halogens, a treatment for removing nitrogen oxides, and adesulfuration treatment.

Generally the installation for treating the gases (113) may thuscomprise a unit for neutralizing the halogens and/or a so-called

DENOX

system allowing catalytic denitrification of the gases notably in thecase when the plasma-forming gas comprises nitrogen, and/or optionally adesulfuration unit.

Neutralization of the halogens present in the form of HCl or of chlorinegas is carried out generally by standard washing with spraying of sodawater according to the following reaction:

HCl+NaOH→NaCl+H₂O,

or according to the following reaction:

Cl₂+2NaOH→NaCl+NaClO+H₂O

Denitrification of nitrogen oxides is for example carried out byreaction with ammonia:

NO+NO₂+2NH₃→2N₂+3H₂O

4NO+4NH₃+O₂→4N₂+6H₂O

2NO₂+4NH₃+O₂→3N₂+6H₂O

In the case when the effluents are loaded with minerals, these gases asthis has already been specified above, pass through a filter placedupstream (112) of the washing system (113).

When the effluents are radioactive, this filter (112) will be of the VHE(

Very High Efficiency

) type.

This type of filter is currently distributed commercially.

Once they are washed, the gases pass through a droplet catcher condenser(114) with which the transport of liquid towards the element (116) andthe chimney (117) may be limited.

The gases circulate in the installation from upstream to downstream bymeans of an extractor (115) maintaining a slight depression in thesystem.

On-line analysis means (118, 119), for example of the infraredspectroscopy or mass spectrometry type, ensure monitoring of the qualityof the gases at the outlet of the cooler (109) and at the chimney (117)in order to determine every time whether the gases may be dischargedinto the atmosphere.

Finally, it should be noted that several plasma torches may be placed ona same reactor. This arrangement may allow treatment of substantial flowrates of fluids and/or simultaneous treatment of different immiscible orchemically incompatible fluids.

Further, the device according to the invention may be a mobile device,placed on a vehicle.

REFERENCES

-   [1] U.S. Pat. No. 4,438,706-   [2] U.S. Pat. No. 4,479,443-   [3] U.S. Pat. No. 4,644,877-   [4] U.S. Pat. No. 4,886,001-   [5] U.S. Pat. No. 5,505,909-   [6] U.S. Pat. No. 5,288,969-   [7] FR-A-2765322-   [8] FR-A-2866414

1. A method for thermal destruction of at least one feed comprising atleast one organic compound by at least one induction plasma formed by atleast one plasma-forming gas ionized by an inductor, wherein thefollowing successive steps are carried out: a) introducing said feedinto the plasma and achieving a supply of oxygen gas in said at leastone plasma-forming gas, and/or in the plasma or in the vicinity of theplasma, by means of which gases are obtained in which decomposition intoatomic elements has been induced; b) in a reaction enclosure, carryingout a first operation for thermal destruction of said gases in whichdecomposition into atomic elements has been induced; c) carrying out asecond operation for thermal destruction of the gases having undergonethe first operation for thermal destruction by mixing said gases withair and/or with oxygen; d) achieving a recombination by cooling at leastone portion of the gases from the mixing; and e) discharging the gasesare discharged.
 2. The method according to claim 1, wherein the supplyof oxygen gas is achieved by using pure oxygen as a singleplasma-forming gas.
 3. The method according to claim 1, wherein theplasma-forming gas(es) is(are) not composed of oxygen, does (do) notcomprise oxygen, or comprise(s) little oxygen, and the supply of oxygengas is achieved by bringing oxygen gas into the plasma or into thevicinity of the plasma.
 4. The method according to claim 3, wherein thesupply of oxygen gas is achieved by introducing oxygen gas into theplasma at a location identical or close to the location where the feedis introduced and simultaneously with the latter.
 5. The methodaccording to claim 3, wherein a molar ratio of the oxygen gas suppliedto the organic compound(s) is greater than a stoichiometric combustionratio.
 6. The method according to claim 1, wherein in step c) the mixingis achieved with a venturi device into which air and/or oxygen gas isinjected.
 7. The method according to claim 1, wherein, when the feedfurther contains at least one mineral filler, in step c), mixing isachieved by an air and/or oxygen distribution ring which injects airand/or oxygen gas towards the main axis of the reaction enclosure. 8.The method according to claim 1, wherein at the end of step d) at leastone step d1) is provided for chemical treatment of the gases.
 9. Themethod according to claim 8, wherein said at least one step d1) forchemical treatment of the gases is selected from the group consisting ofa dehalogenation or neutralization step, a step for deoxidation ofnitrogen oxides, and a desulfuration step.
 10. The method according toclaim 8, wherein the feed further comprises at least one mineral fillerand a gas filtering step is provided after step d) and before step d1).11. The method according to claim 8, wherein at the end of the step forchemical treatment of the gases d1), the gases are treated in a dropletcatcher condenser.
 12. The method according to claim 1, wherein severalidentical or different feeds are treated with several plasmas.
 13. Adevice for destruction of at least one feed comprising at least oneorganic compound by at least one induction plasma formed by at least oneplasma-forming gas ionized by an inductor, comprising: at least oneinductive plasma torch; means for introducing at least oneplasma-forming gas into said torch; optionally means for bringing oxygengas into the plasma or into the vicinity of the plasma; means forintroducing said feed into said torch; a reaction enclosure capable ofallowing thermal destruction of the gases flowing out of the inductiveplasma torch; a device allowing mixing of the gases flowing out of thereaction enclosure to be carried out; means for introducing air and/oroxygen gas into the mixing device; a device allowing recombination bycooling of at least one portion of the gases from the mixing device; theinductive torch, the reaction enclosure, the mixing device and therecombination device being in fluidic communication.
 14. The deviceaccording to claim 13, wherein the means for introducing the feed intothe torch consist of a tube made of a refractory material, the inside ofwhich is packed with a textile made of fibers of a refractory material.15. The device according to claim 14, wherein said tube made of arefractory material further comprises in its center a tube for bringingoxygen gas into the plasma.
 16. The thermal destruction device accordingto claim 13, wherein the device allowing mixing of the gases to beachieved is a venturi.
 17. The thermal destruction device according toclaim 13, wherein the device allowing mixing of the gases to be carriedout is a distribution ring which is capable of injecting air and/oroxygen towards the main axis of the reaction enclosure.
 18. The thermaldestruction device according to claim 13, wherein it further comprises,located downstream from the gas recombination device in the direction ofthe circulation of the gases, at least one device allowing chemicaltreatment of the gases from the recombination device.
 19. The thermaldestruction device according to claim 18, wherein said at least onedevice allowing chemical treatment of the gases from the recombinationdevice, achieves at least one reaction selected from a dehalogenation, adeoxidation of nitrogen oxides and a desulfuration.
 20. The deviceaccording to claim 18, wherein it further comprises filtering meansdownstream from the gas recombination device in the direction of thecirculation of the gases, and upstream from said at least one deviceallowing chemical treatment of the gases from the recombination device.21. The device according to claim 13, which comprises several plasmatorches.
 22. The device according to claim 13, wherein it is placed on avehicle.